Selective flotation of chromite ores



Patented Mey 1o, 1949 UNITED STATES PATENT OFFICE 2,469,422 .SELECTIVE FLOTATION OF CHBOMITE DRES Arthur J. Weinig, Golden, Colo. Application December 20, 1943, Serial No. 514,987 4 Claims. (Cl, 209-167) This invention relates to a froth flotation treatment of chromite ores, and more particularly relates to the treatment of chr-omite beach sands, or the treatment of the product of a gravity concentration of such beach sands.

Deposits of the aforesaid character occur in a variety of places. As an example, chromite beach sands of Coos County, Oregon have been found to be particularly amenable to the present treatment. A variety of minerals are contained in such sands, as for example, chrome, spinels, Zircon, staurolite, ilmenite, magnetite,

garnet as wel1 as a quartz, epidote, olivine and its alteration products.

In the case of beach sands the chromite content is rather small, the aforesaid Coos County, Oregon sands having a CrzOa content of about 6%. Due to long weathering and exposure, the mineral surfaces have been altered to such an extent that the material will not respond to conventional froth flotation treatments. Further, because of the low chrome 'content expensive processing is not feasible for commercial op erations.

It is an object of the present invention to provide a simple,-eiiicient and economica1 froth fiotation process for the treatment of chromite ores providing a selective recovery of the chromite and/or other valuable constituents of the ores.

Another object of the invention is to-provide a froth flotation treatment of chromite ores in which the solution of the pulp may be recovered and recirculated through the treatment stage in which it initially was used.

.A further object of the invention is to provide a novel procedure for the apportioning of the reagent ingredients used in a froth flotation treatment of chromite ores.

Other objects of the invention include novel steps and treatments, all of which will be fully described in the course of the following description.

Briefly stated, the invention comprises an initial bulk flotation filming of the constituent minerals in the presence of a iluosilicate-forming composition, partially neutralizing the resulting acidifled surfaces to a degree which will permit flotation collectors to produce flotation, and then partially acidifying again to promote selective notation of different minerals of the composition. When so conditioned, the selected minerals of the pulp will respond readily to the action of a fatty acid collector under the influence of aeration and carry to the surface in a froth where they may be removed by overflow.

In order to effectively acidify and neutralize the particle surfaces, particularly when a continuous operation is employed, an exact test procedure has been developed for use in performing the flotation process. This procedure will be best understood by describing a typical test operation treating a gravity concentrate of Coos County, Oregon, beach sands.

1500 ml. water and 0.5 gram of sodium silicoiiuoride were introduced into a 500 gram mechanical laboratory flotation machine. This composition was agitated and then 25 ml. of the mixture was'titrated with a caustic soda solution (equivalent to 8.66 gr. oxalic acid per litre). The ml. used multiplied by 0.4 will indicate the equivalent acidity in pounds of Ca(OH)2 per ton of solution. This should be around .4 lb.

Ca( OH) 2 per ton of solution.

750 to 1000 grams of a gravity concentrated chrome ore at 48 mesh and containing about 25% CrzOa was introduced into the above solution and agitated or blunged for fifteen minutes with no aerating gas introduced. When agitation was stopped 25 ml. of the upper solution was drawn off, a phenol indicator added, and titrated with the caustic soda. solution. Only a slight drop in the titration should be noted, probably not below .36 Ca(OH)2 per ton of solution.

Thereafter, the following reagents were introduced into theconditioned pulp in the amounts and orders stated:

1. .6 ml. 30% aqueous solution of caustic soda (300 grams per litre) about '1.5 normal.

2. 10 drops gas oil or crude kerosene.

3. 10 drops of petroleum aliphatic acid (Standard Oil Co. of California No. 30395-R) 4. 20 ml. of a 5% solution formed by treating 50 ml. distilled talloel with 20 m1. ammonia sol. (25 B.) and diluting with 1000 c. c. water.

After this conditioning, the air was turned on and the froth skimmed 01T after aerating for one to two minutes. The machine then was emptied, the liquid decanted and the separated solution saved. The reject tailings of this separation were quartz, epidote, olivine and alteration products together with some garnet.

, the solution of this Next. the froth 'concentrate was returned to the machin mixed with the decanted solution, agitated for two minutes, after which 2 ml. aqueous sulfuric acid solution was added. The air was turned on and the froth concentrate removed after aerating one to two minutes. The residue again was decanted, and theA tailings, in this case clear garnet, were removed.

Following this two stage separation, a third separation was made to produce a higher grade chromite concentration. The froth concentrate 'of the preceding separation was returned to the machine. mixed with the decanted solution with 1,m1. aqueous sulfuric acid solution and 15 ml. of 5% quebracho extract added and then reiloated.

The tailings of this treatment include additional varieties of garnet, zlrcon, magnetite, ilmenite and chrome spinels, staurolite etc., which should be classed as a middling. Titration of operation should endln a blue reaction color instead of a pink. The titration should be about .6 to .7.

With. this understanding of the operatingprocedure to be followed in the practice of the present invention, some typical tests will be cited to illustrate the efficiency of the treatment. In the first of these, the ore taken for test was a gravity concentrated beach sand which assayed 26.5% CriOa. The treatment performed was a substantial duplicate of that enumerated hereinbefore. The results follow:

A similar treatment of another ore sample of gravity concentrated beach sand assaying 28% CrrOa was undertaken and the results follow:

Test 2 Percent Percent Percent Product Wt Wt. CHO; Recovery Concentrate 650 65. 0 41:8 97. 5 Tails 350 35. 0 l. 0

Total l, 000

A third test was understaken with additional ore from the same sample as used for Test 2. The results of the treatment follow:

Gil

The final concentrate was 57% by weight and analyzed 45.4 CrzOs.

The concentrate made in this test was subjected to fractional magnetic separation with the following results:

A study of these magnetic fractions leads us to conclude that a chrome concentrate of about 52%-Cr203 grade is the ultimate which can be made. Aside from the evident magnetite and ilmenite present there are chrome spinels present of various CrzOs content and these minerals must be dropped out to attain maximum grade at the expense of recovery.

From the foregoing, it will be apparent that by subjecting a pulp, inclusive ofl concentrates from a preceding operation, to a succession of flotation actions with an increase in acidity at each successive lstage,`it is possible to reject minerals of the pulp until only a puried chromite is collected as froth concentrate.

In the aforesaid tests, the treatment procedure has involved batch methods, but it will be apparent that the process can be performed effectively as a continuous operation. In such a treatment, conditioning .tanks will be placed ahead of each flotation section and the required conditioning interval can be maintained at each stage. Also, once the requirements of a given operation are known, the acidity changes can be closely regulated with periodic reagent introduction at each conditioning stage.

Where the liquid of the pulp is to be recirculated, it will be desirable because of the acidity regulation to only introduce such liquid into whatever flotation battery it has been withdrawn from. To do otherwise would upset the acidity controls, which are quite important in obtaining the desired selective action. A convenient means for dewatering the pulp after collection of the concentrate at a given stage is to direct the tailings discharge into a mechanical type classifier. The various sands are relatively heavy and settle quite easily, so that a substantially clear liquid is passed across the overilow of the classifier and the raked product can be removed as a reject material or collected as a market product according to its composition and market value.

Test 3 Analyses Product Wh Percent Percent Wt' Percent Percent Percent Recovery CHO; FSO Tio! Concentrate 455 57 45.4 26.75 1.9 92 s 295 43 5.35

Total 750 A variety of reagent compositions have been tested and numerous substitute materials have been found to be suitable for use in the process. In the initial blunging treatment a number of compositions have given good results. I have described the use of sodium Silico fluoride, and, in

such as sodium biiiuoride, sodium fluoride and hydroiiuoric acid may be used. These various iluorsilicate-forming ingredients serve to condition the material for a bulk flotation action, after which by neutralizing to a degree where only quartz, epidote, olivine and alteration products will be rejected a concentrate is produced by froth floating in the presence of a fatty acid collector. In this action, I prefer to usefan oil such as crude kerosene or gas oil to promote the filming. Almost any fatty acid soap will function as a collector reagent if the proper acid conditions for such soap are established in thetreatment. I preferably use a fatty acid with three double bonds such as an ammonium salt of linoleic or ammonium linoleate. Beneficial results are derived if a frother is used, and petroleum aliphatic acids, steam distilled pine oil or cresylic acid may be used for this purpose.

In operations where a high degree of selectivity is desired, I introduce into the nal flotation stage an additional reagent such as a quebracho extract or lignin, tannic acid or its derivatives, and thereby impede the flotation of all minerals except the chromite. Due to the stage flotation treatment employed and the elimination of constitutent minerals at each stage, it will be apparent that a substantial amount of the CraOa content will be eliminated by such procedure. The nal product is a purified chromite containing very little material that may be classed as contaminant, but whenever such a purified product is not required, the recovery can be raised by reducing the selectivity of the treatment.

The accompanying flowsheet illustrates a typical circuit used in the practice of the present invention. As illustrated, a conditioner tank I is supplied with a, suitable chromite ore pulp in troduced at 2 while sodium Silico-fluoride is fed addition, various laundry sours or iiuoride sours.

in at 3 to produce an acidity condition in the pulp equivalent to .40 lb. Ca(OH) 2 per ton of solution. When so conditioned the pulp is discharged at d into a second conditioning tank 5 in which a mixture of caustic soda, kerosene, petroleum aliphatic acid frother and ammonia talleol mixture are fed to the pulp at 6 to produce an acidity equivalent to .08 to .16 lb. Camif) 2 per ton of solution.

The pulp so conditioned is discharged at 1 into a flotation cell or stage where enough mineral acid, preferably sulfuric acid, is introduced at 9 to bring the acidity of the pulp within the equivalent range of from .G3 to .05 lb. per ton of Ca(OH)2 Der ton of solution. A bulk flotation of the chromite is obtained in cell 8' with the reject material consisting of quartz, epidote, olivine and alteration products being discharged at ld while the collected froth is overowed at Il. The tailings pass into a thckener l2 with the sludge discharge it thereof passing to Waste While the clarified liquid is drawn from the thickener overiiovsr4 i3 and passes to a second flotation stage I5 in which the froth overilow from Il also is introduced together with additional sulfuric acid as indicated at i6 to produce a pulp acidity equivalent to .50 lb. Ca(OH)2 per ton of solution. The collected froth concentrate is removed by overflow at il and the reject tailings pass I through a line i8 into a thickener id from which the sludge discharge of which garnet is the principal constituent may be collected as a concentrate.

The claried liquid collected in thickener I9 passes through a line 2| to another flotation stage 22 in which the froth concentrate from I1 ls delivered and in which additional mineral acid is introduced as at 23 to produce a pulp acidity equivalent to .55 lb. Ca(OH)z per ton of solution. The tailings reject of this stage, consistlng principally of middlings, is discharged at 24 and may be and preferably is returned to the initial flotation stage 8 while the froth concen trate is overiowed at 25 and passes into another flotation stage 26. A quantity of quebracho extract is introduced into this pulp which by further acidity control is maintained at an acidity equivalent to .6 5 lb. Ca(OH)2 per ton of solution.l The collected froth is discharged at 28 as the iinal chrome concentrate, while the tailings reject consisting of various chrome-containing minerals may be taken on to further treatment. if desired, or may be handled as a bulk concentrate. k

The flow sheetvjust described is particularly suited for the performance of the present process in continuous operation. However, it should be understood that'variations in the circuit are intended to suit commercial requirements. Thus,

if the rejection of quartz, olivine, epidote and the like with the tailings at flotation stage 8 produces a market grade concentrate, it may be necessary to follow with only one additional flotation treatment to separate garnet from chrome and obtain the final market products. Also in batch operations a single notation stage may be adequate, and by selective acidity control a plurality of nal products may be obtained.

I have described the treatment of Gregori beach sands, but it will be understood that the same treatment procedure with proper readjustment may be followed with equally good results in treating mined chromite ores. Where freshly mined ores are taken for treatment, the initial blunging treatment may be shortened or eliminated if there are no altered surfaces that have to be acted upon, and preferably such a blunging treatment will follow the grinding stage of thetreatment. Where closed circuit grinding is practiced, the classifier overow may be conducted to suitable agitating or conditioning apparatus in which the laundry sours will be introduced.

The flotation treatments may be performed in suitable froth dotation apparatus, and preferably in mechanical type :dotation machines. The treatment interval is of relatively short duration as the mineral noats quite readily after the conditioning hereinbefore described.

Changes and modifications may be availed of within the spirit and scope of the invention as dened in the hereunto appended claims.

What I claim and desire to secure by Letters Patent is:

1. A selective froth dotation process for the treatment of chromite ores havin'g low grade chrome spinels, Zircon, staurolite, ilmenite, magnetite, garnet, quartz, epidote, olivine and alteration products as inclusions, which comprises subjecting a pulp of such an ore to an initial blunging4 treatment in the presence of a soluble iuosilicate-forming substance, partially neutralizing the acidified particle surfaces by introducing a caustic into the pulp, subjecting said pulp to a bulk froth notation action in the presence of a fatty acid collector to concentrate the chrome-containing constituents of the pulp, refloating the concentrate of the treatment in a plurality of cleaning actions while increasing the acidity of the pulp in each such refioating action through the introduction of a mineral acid therein, whereby to selectively reject dierentl minerals of the pulp, and recovering a purified chromite concentrate as a ilnal product of the treatment. v

2. A selective froth flotation process for the treatment of chromite ores having low grade chrome spinels, zircon, staurolite, ilmenite, magnetite, garnet, quartz, epidote, olivine and alteration products as inclusions, which comprises subjecting a pulp of such an ore to an initial blunging treatment in the presence of a soluble iiuosilicate-forming substance, partially neutralzing the acidied particle surfaces by introducing a caustic into the pulp, subjecting said pulp to a bulk froth flotation action in the presence of a fatty acid collector to concentrate the chrome-containing constituents of the pulp, refioating the concentrate of the treatment in a plurality of cleaning actions while increasing the acidity of the pulp in each such reiloating action through the introduction of a mineral acid therein, whereby to selectively reject different minerals of the pulp, recovering a purified chromite concentrate as a final product of the treatment, and recovering a garnet residue from .one of said treatment stages as another Vfinal product of the treatment.

3. A selective froth flotation process for the treatment of chromite ores having low grade chrome spinels, Zircon, staurolite, ilmenite, magnetite, garnet, quartz, epidote, olivine and alteration products as inclusions, which comprises subjecting a pulp of such an ore to an initial blunging treatment in the presence of a soluble fluosilicate-forming substance, partially neutralizng the acidied particle surfaces by introducing a caustic into the pulp, subjecting said pulp to a bulk froth flotation action in the presence of a fatty acid collector to concentrate the chrome-containing constituents while rejecting quartz, epidote, olivine and alteration products. increasing the acidity of the pulp by entering a quantity of mineral acid into the froth concentrate product so formed, refloating said concentrate in a second froth flotation action to reject garnet, entering additional mineral acid into the froth concentrate of said second action, reiloating said second concentrate in a third froth flotation action to reject magnetite. ilmenite, staurolite, zircon and low grade chrome spinels, and collecting puried chromite 'as a final froth concentrate ofthe treatment.

4. A selective froth flotation process for the treatment of chromite ores having low grade chrome spinels, zircon, staurolite, ilmenite, magnetite. garnet, quartz, epidote, olivine and alteration products as inclusions, which comprises subjecting a pulp of such an ore to an initial blunging treatment in therpresence of a soluble iluosilicate-forming substance, partially neutralizing the acidied particle surfaces by introducing a caustic into the pulp, increasing the acidity of the pulp by introducing some mineral acid therein, subjecting saidpulp to a froth flotation action in the vpresence of a fatty acid collector to concentrate the chrome-containing constituents while rejecting quartz, epidote, olivine and alteration products, entering additional mineral acid into the froth concentrate product so formed, subjecting said concentrate product to another froth flotation treatment to collect the other chrome-containing constitutents while rejecting garnet. removing the reject garnet product as a concentrate of the treatment, entering additional mineral acid into the froth concentrate of said second action and refloating said second concentrate in a third froth flotation action in which at least one of the chromecontaining constituents consisting of magnetite,

ilmenite, staurolite, Vzircon and low grade spinels is rejected.

ARTHUR J. WEINIG.

REFERENCES CITED The following references are of record in the nle of this patent:

UNITED STATES PATENTS Number Name Date 1,972,588 Hansen Sept. 4, 1934 1,986,816` Hallestrom Jan. 8, 1935 2,014,404 Weed Sept. 17, 1935 2,125,631 Gutzeit Aug. 2, 1938 OTHER REFERENCES Conditioning Surfaces for Flotation, by Norman 8: Ralston in Mining Technology, May 1939, T. P. 1074, pages 1, 2, 3, 4, 5, 11, 12, 13, 15, 16.

Control of the Souring Operation, by B. H. Gilmore, Special Bulletin, February 1931, Laundry (g-visirs, National Asso., pages 3 and 4, copy in 

